Crossed-field discharge device and improved magnetic pole structures therefor



Aug. 5, 1969 J. E. STAATS 3,459,994

CROSSED-FIELD DISCHARGE DEVICE AND IMPROVED MAGNETIC POLE STRUCTURESTHEREFOR Filed Oct. 6, 1966 4 Sheets-Sheet l FIGJ 236a 227 INVEN TORJAMES E. STA/1T5 BY VWIQATTYS.

Aug. 5, 1969 .J. E. STAATS 3,459,994

CROSSED-FIELD DISCHARGE DEVICE AND IMPROVED v MAGNETIC POL-I3 STRUCTURESTHEREFOR Filed Oct. 6, 1966 4 Sheets-Sheet 2 FI6.'2' Y Aug. 5, 1969 J.E. STAATS 3,459,994

CROSSED- P 1 I E L D D I SCHARGE DEVICE A N D I M P R 0 VEL) MAGNETICPOLE STRUCTURES 'I'I'HERYHOR Filed Oct. 6. 1966 4 Sheets-Sheet L;

Aug. 5, 1969 J. E. STAATS 3,459.994

CROSSED-FIELD DISCHARGE DEVICE AND IMPROVED MAGNETIC POLE STRUCTURESTHEREFOR Filed Oct. 6, 1966 4 Sheets-Sheet 4 I *1 /44 I 5 I06 7 l. ,06/45 United States Patent Ofiice US. Cl. 31539.71 16 Claims ABSTRACT OFTHE DISCLOSURE There is disclosed a crossed-field discharge devicecomprising an envelope enclosing an anode structure which defines anaxially extending space, an electron emissive cathode structure disposedin the axially extending space and a pair of identical composite polepieces disposed adjacent to the opposite ends of the anode structure,each composite pole piece including an inner annular pole piece disposedinternally of the envelope and an outer annular pole piece disposedexternally of the envelope in radial alignment with the inner polepiece, the outer diameter of the composite pole piece being from about2.0 to about 2.5 times the axial gap between the internal pole pieces.

The present invention relates to an improved crossedfield dischargedevice and particularly to an improved magnetic pole structure therefor,and to microwave assem'blies incorporating the improved crossed-fielddischarge device therein.

It is a general object of the invention to provide a new and improvedcrossed-field discharge device for use at microwave frequencies, whichdevice incorporates therein an improved magnetic pole structureproviding a more uniform field through the interaction space all in acompact and inexpensive crossed-field device.

Another object of the invention is to provide an improved cross-fielddischarge device comprising an envelope an anode structure disposed inthe envelope and defining an axially extending space, an axiallyextending cathode structure disposed in the axially extending space andcooperating with the anode structure to define an axially extendingannular interaction space therebetween, the cathode structure includingan electron emissive element disposed within the anode structure andadjacent to the inner portion of the interaction space, a pair ofinternal magnetic pole pieces disposed interiorly of the envelope andrespectively arranged adjacent to the opposite ends of the anodestructure for establishing a unidirectional magnetic field extendingaxially through the interaction space, and a pair of external magneticpole pieces disposed exteriorly of the envelope and respectivelyarranged adjacent to the internal pole pieces and in surroundingrelation therewith and extending radially outwardly therefrom, each oneof the internal pole pieces cooperating with the adjacent one of theexternal pole pieces to provide a composite pole piece, the dimensionsof the composite pole pieces normal to the axis of the interaction spacebeing substantially greater than the gap between the internal polepieces axially through the interaction space.

Another object of the invention is to provide a crossedfield dischargedevice of the type set forth, wherein the portions of the wall of theenvelope disposed between adjacent ones of the pole pieces in each ofthe composite pole pieces is of lesser thickness than the remainingportions of the wall of the envelope to decrease the magnetic reluctancebetween the adjacent ones of the pole pieces in each of the compositepole pieces.

Another object of the invention is to provide a crossed- 3,459,994Patented Aug. 5, 1969 field discharge device of the type set forthwherein each of the internal pole pieces and each of the external polepieces has an axially extending annular [flange thereon disposed againstthe envelope, the flange on each of the internal pole pieces beingdisposed in radial alignment with the flange of the adjacent one of theexternal pole pieces.

Another object of the invention is to provide a crossed-field dischargedevice of the type set forth wherein each of the internal magnetic polepieces has a generally circular periphery and each of the externalmagnetic pole pieces has a generally circular periphery, the internalpole pieces also preferably being disposed respectively at the oppositeends of the envelope and providing the end caps therefor.

In connection with the foregoing object, it is another object of theinvention to provide an improved crossedfield discharge device of thetype set forth wherein the ratio between the diameter of the compositepole pieces normal to the axis of the interaction space and the gapbetween the internal pole pieces axially through the interaction spaceis in the range from about 2.0:1 to about 2.5:1.

A further object of the invention is to provide a microwave assemblyincorporating therein the improved crossed-field discharge device of thepresent invention, the device also being provided with a plurality ofradially extending cooling fins mounted on the envelope in good thermalcontact therewith, a pair of annular field coils disposed with the axesthereof in alignment with the longitudinal axis of the interaction spaceand respectively arranged adjacent to the opposite ends of the devicefor establishing a unidirectional magnetic field therebetween, a

cooling fins, a pair of outer sections disposed on opposite sides of theassociated field coil and magnetically coupled to the end section andextending toward the device and terminating at points spaced outwardlyand well away from the associated external pole piece, and side walls ofnon-magnetic material interconnecting the opposed pairs of the outersections, the end sections and the outer sections and the side wallscooperating to provide a box-like structure open on two opposed sidesthereof and defining a passage for cooling air passing therethrough andover the cooling fins and around the device to cool the same.

A still further object of the invention is to provide a microwaveassembly of the type set forth wherein the cooling fins and the endsections have substantially rectangular peripheries and the outersections are disposed on opposed sides of the rectangular end sections,the cooling fins being formed of copper and the side walls being formedof aluminum.

Further features of the invention pertain to the particular arrangementof the parts of the crossed-field discharge device and the mountingthereof in the microwave assembly, whereby the above-outlined andadditional operating features thereof are attained.

The invention, both as to its organization and method of operation,together with further objects and adavantages thereof, will best beunderstood by reference to the following specification when taken inconnection with the accompanying drawings, in which:

FIGURE 1 is a view in vertical section through a microwave assemblyincorporating therein a crossed-field discharge device of the presentinvention, there being illustrated and associated with the devicemagnetic field coils therefor and the magnetic return structure and airduct housing therefor and the coupler and filter construction usedtherewith;

FIG. 2 is an enlarged view in vertical section through the crossed-fielddischarge device illustrated in FIG. 1;

FIG. 3 is a view in horizontal section through the assembly of FIG. 1along the line 33 thereof;

FIG. 4 is a fragmentary view in horizontal section through the device ofFIG. 2 along the line 4-4 thereof; and

FIG. 5 is a view in vertical section through the device of FIGS. 1 and 2and illustrating more fully the relationship between the diameter of thecomposite magnetic pole pieces and the length of the gap between thepole pieces axially through the interaction space.

Referring to FIGS. 1 and 2 of the drawings, there is illustrated amicrowave generator embodying the features of the present invention, themicrowave generator 10 more particularly including the improvedcrossed-field discharge device 100 of the present invention. The device100 comprises an anode structure 101 including a sleeve 102 and a pairof anode members 110, a cathode structure 150, a pair of opposed polepieces 130, an upper end structure 180 and a lower end structure 190.

The anode structure 101 is essentially annular in shape and is confinedwithin the interior of the sleeve 102 (see FIGS. 2. and 5), the sleeve102 being generally tubular and having a circular cross section at allpoints therealong, the outer surface 103 thereof being cylindrical. Theinner surface 104 of the sleeve 102 is also cylindrical in shape and hasat each end thereof a recess to define upper and lower end Walls 102 andupper and lower side walls 106 of reduced thickness, the end walls 105being essentially annular in shape and disposed parallel to each otherand normal to the axis of the device 100 the side walls 106 beingannular in shape and extending axially of the device 100. Mounted on thesleeve 102 at essentially the midpoint thereof and extending outwardlytherefrom is an exhaust tubulation 107 hermetically sealed thereto andcommunicating with the interior thereof, the exhaust tubulation 107being useful to evacuate the device 100, the interior of the device 100being evacuated to a high degree and being hermetically sealed as willbe explained more fully hereinafter. Also mounted on the outer surface103 of the sleeve 102 is a stacked array of cooling fins 108, each ofthe cooling fins 108 being provided with an annular flange 109 thatextends around the sleeve 102 and is fixedly secured thereto as bybrazing. It will be understood that the sleeve 1-02 and the fins 108 areformed of a metal having good thermal conductivity, the preferredmaterial being copper, thereby to accommodate the conduction of heatfrom the device 100 outwardly therefrom and into the fins 108. The shapeof the fins 108 is substantially rectangular so that they fit within abox-like structure 200 disposed therearound, there preferably beingprovided means for passing a cooling fluid, such as a stream of air,through the box-like structure 200 and over the fins 108 to effectcooling thereof and a consequent removal of heat from the device 100during the operation thereof.

Disposed within the sleeve 102 and also forming a part of the anodestructure 101 are the two anode members 110. Referring particularly toFIGS. 2, 4 and 5, there is illustrated in detail the construction of theanode members 110. As illustrated, each anode member 1 10 is generallyannular in shape and includes a body portion 111 disposed at one endthereof (the upper end as viewed in FIG. 2), the body portion 111 havingan outer end wall 112 at one end thereof connecting with an annularouter wall 113 having an outer diameter only slightly less than theinner diameter of the sleeve 102, and specifically the inner surface 104thereof, whereby the anode member 110 can fit within the sleeve 102 andultimately is connected thereto as by brazing. The end of the bodyportion 111 opposite the end wall 112 is cut away or recessed to providean annular inner Wall 114 extending therearound and concentric with theannular outer wall 113 but having a substantially smaller diameter, thewalls 113 and 114 being joined by an annular end wall 115 disposedparallel to the outer end wall 112 and normal to the walls 113 and 114;the other end of the inner wall 114 connects with an inner end wall 116that defines the other end of the body portion 111, the end wall 116being disposed in a plane parallel to the end walls 112 and 115 andnormal to the walls 113 and 114.

There is provided interiorly of the anode member 110 and extending thelength of the body portion 111 a plurality of axially extending anodesegments 117 that project radially inwardly into the axially extendingspace within the anode member 110 and providing therebetween acorresponding plurality of axially extending anode recesses 122, fifteenof the anode segments 11 7 and fifteen of the corresponding recesses 122being provided in the anode member 110 as illustrated. Each of the anodesegments 117 has an axially extending inner surface 118 and a pair ofoutwardly directed side walls 119 on the opposite sides thereof, thecircumferential extent of the inner surface 118 being substantially lessthan the radial extent of the associated side walls 119. The outer endsof adjacent pairs of the side walls 119 are joined by an outer wall 121,whereby the recesses 122 are defined by the associated side walls 119and the associated outer wall 121, the side walls 119 of each recess 122converging inwardly and being disposed substantially normal to theassociated outer walls 121.

The anode member 110 further has thereon and integral therewith fifteenrods or vanes 125, each of the rods 125 being integral with andextending longitudinally from one of the anode segments 117. Morespecifically, the inner surface 118 of each of the anode segments 117extends forwardly beyond the inner end wall 116 and substantiallyparallel to the axis of the anode member 110 and forms the inner surfaceof the associated rod 125. A portion of the side walls 119 on the anodesegment 117 also extends forwardly beyond the inner end wall 116 toprovide the radially extending sides of the associated rod 125, theinner surface 118 and the side walls 119 terminating at an end 126disposed substantially normal to the axis of the anode member 110. Anouter surface 127 is provided for each of the rods 125, the outersurface 127 extending from the inner end wall 116 forwardly to the rod126; more specifically, the inner end of the outer surface 127 joins theinner end wall 116 at a point spaced radially inwardly away from theadjacent outer walls 121 (see FIG. 4) and tapers inwardly toward theassociated inner surface from the end wall 116 to the rod end 126.

The anode members 110 are also formed of a metal having good thermalconductivity, the preferred material being copper. The sleeve 102 andthe anode members 110 also must have good electrical conductivity, thecopper providing the necessary good electrical conductivity as well asthe good thermal conductivity. As illustrated in FIGS. 2 and 5, one ofthe anode members 110 is disposed in the upper portion of the sleeve 102with the body portion 111 thereof disposed upwardly and with the rods125 thereof extending downwardly; the other one of the anode members 110is disposed in the lower portion of the sleeve 102 with the body portion111 thereof disposed downwardly and with the rods 125 thereof extendingupwardly. As is also illustrated in FIG. 4, the anode members 110 arerotated slightly with respect to each other so that the anode rods 125on one of the anode members 110 are disposed in the center of therecesses 12 of the other one of the anode members 110, and converselythe anode rods 125 on the other one of the anode members 110 aredisposed in the center of the recesses 122 of the one anode member 110.In this arrangement, there is one of the anode rods 125 disposed in eachof the anode recesses 122 and equidistantly spaced from the adjacentanode segments 117, all as is diagrammatically illustrated in FIG. 4.

The sleeve 102 and the anode members 110 also cooperate to provide anouter axially extending space 120, the space 120 being annular in shapeand bounded on the outer portion by the inner wall 104 of the sleeve 102and on the inner portion by the inner walls 114 and at the upper andlower ends by the end walls 115. The interior of the anode members 110form a second or inner axially extending space Within which is disposedthe cathode structure 150, the space between the outer surface of thecathode structure 150 and the spaced facing surfaces 118 defining anannular axially extending interaction space 160. Furthermore, the innerend walls 116 are spaced apart to provide therebetween a radiallyextending annular passage 123 interconnecting the outer space 120 at themid-portion thereof to the inner axially extending space at themidportion thereof and to the interaction space 160 at the mid-portionthereof.

The cathode structure 150 is provided in the axially extending spacedefined by the anode members 110, the cathode structure 150 including acylindrical metal wall 151 (see FIG. 4) arranged with the axis thereofdisposed at the axis of the device 100, the wall 151 being formed of aheat resistant and electrically conducting metal, the preferred materialof construction being nickel. Mounted on each end of the wall 151 is acathode end 152, the cathode ends 152 being substantially identical inconstruction, whereby the same reference numerals have been applied tolike parts of both. Referring to the upper cathode end 152, it includesa substantially flat annular center plate 153 carrying on the outer edgethereof an axially directed annular inner flange 154 carrying on theinner end thereof an outwardly directed flat flange 155; the outerperiphery of the flange 155 carries a mounting flange 156 thereonextending outwardly and disposed within the adjacent end of the wall 151and suitably secured thereto as by welding. The outer edge of the flange156 carries a radially and outwardly extending shield flange 157 thatextends radially outwardly beyond the wall 151 and overlies the adjacentend of the interaction space 160. Each center plate 153 has a centralopening 158 therein, the lower cathode end 152 carrying on the inneredge and surrounding the opening 158 therein a center end flange 159.The cathode ends 152 are also preferably formed of nickel. The uppercathode end 152 is mechanically and electrically connected to a cathodestud 167, the cathode stud 167 being generally circular in cross sectionand having at the lower end thereof a reduced diameter portion 168 thatextends through the opening 158 in the cathode end 152 and is fixedlysecured thereto as by a pair of outwardly directed flanges 169. It willbe appreciated that the upper end of the cathode structure 150 is bothelectrically and mechanically connected to the stud 167.

The cathode wall 151 is provided with a sintered porous coating 161impregnated with a suitable electron emissive oxide material, wherebyupon heating of the cathode structure 150, the coating 161 readily emitselectrons from the outer surface thereof. Referring particularly to FIG.4, it will be seen that the coating 161 is shaped to provide a pluralityof outwardly extending projections 162 each having outwardly convergingside walls joining a generally circumferentially arranged outer surface163, a space 164 being provided between the adjacent projections 162. Asillustrated, the circumferential extent of the outer surface 163 issubstantially equal to the space 164 between the adjacent projections162. The preferred range of the circumferential extent of each of theouter surfaces 163 is approximately 25% to approximately 60% of thecircumferential distance between the centers of adjacent outer surfaces163. The number of projections 162 provided on the coating 161 is equalto the sum of the number of the anode segments 117 and the number ofcooperating rods 125, whereby there are thirty of the projections 162provided upon the coating 161. The outer surfaces of the coating 161together with the inner surfaces 118 on the anode members 110, definethe interaction space 160 disposed therebetween in which the emittedelectrons from the coating 161 interact with the electrical fields andthe magnetic fields disposed between the anode structure 101 and thecathode structure 150. The projections 162 combine with the anodesegments 117 and with the rods 125 to provide a preferred distributionof the several fields within the interaction space 160 of the devicethat results in more desirable operating characteristics thereof. Oneparticularly desirable result of the shape of the coating 161 is theminimized back heating of the cathode structure 150', the desirableemitted electrons emanating from the projections 162, and theundesirable emitted electrons emanating from the space 164 between theprojections 162, thereby to facilitate the emission of desirableelectrons and to suppress the emission of undesirable electrons.

It further will be noted from FIG. 4, that the center line of eachprojection 162 is circumferentially displaced relative to the centerline of its corresponding anode segment 117 or its corresponding rod125, as the case may be; more specifically, the center lines of theprojection 162 are displaced in a clockwise direction a circumferentialdistance equal to approximately 40% of the circumferential spacingbetween the center lines of an adjacent anode segment 117 and anadjacent rod (for example 5 rotation for a 12 spacing or a percentage of41.8% as illustrated). The circumferential displacement of theprojections 162 with respect to the corresponding anode segments or rodsis preferably in the range between 0% and approximately 45% of thecircumferential spacing between adjacent anode segments and rods, thepreferred range being between approximately 25% and 45% of the spacingbetween adjacent anode segments and rods, a still more preferred rangebeing between approximately 35% and 45% of the spacing between adjacentanode segments and rods. Furthermore, the displacement is on thedownstream side, i.e., in the direction of normal initial electron flowfrom the projections 162. It also will be noted that the electronemissive coating 161 is confined between the outer end walls 112 of theanode members 110, the cathode structure being carefully centered withrespect to the anode members 110, whereby each of the cathodeprojections 162 extends axially of the device 100 parallel to the axisthereof and confined between the outer end walls 112.

The radial dimension of each of the projections 162 varies from end toend of the cathode structure 150. Adjacent to the outer ends of thecathode structure 150, the radial dimensions of each of the projections162 is preferably greater than about 20% of the spacing between theanode surfaces 118 and the coating 161 on the cathode structure 150. Atthe longitudinal midpoint of the emissive coating 161, an area 166 ofreduced radial dimension is provided, the radial extent of theprojections 162 being substantially nil and in certain instances thecoating 161 being completely removed at the center reduced portion 166;the portion 166 is opposite the annular passage 123 between the anodemembers 110 and is provided at this point to match impedances at thisarea in the device 100. There further is provided an intermediatereduced portion 165 between the center reduced portion 166 and each ofthe outer ends of the cathode structure 150, the intermediate reducedportions 165 having roughly one-half of the radial extent of theprojections 162 therein that are found at the outer ends of the coatings161. The longitudinal extent of the outer coating portions issubstantially equal to the longitudinal extent of the intermediatereduced portions 165, which is in turn substantially equal to thelongitudinal extent of the center reduced portion 1'66. In a typicalconstruction of the coating 161, the

difference in the thickness of the coating is approximately mils fromone section to the adjacent section of the coating 161.

As illustrated, the cathode structure 150 is of the indirectly heatedtype, and accordingly, there has been provided within the cathode wall151 a heater 176 in the form of a coiled filament extendingsubstantially the entire length of the cathode wall 151 and spacedinwardly a short distance from the inner surface thereof. The upper endof the heater 176 as viewed in FIG. 2 has an outer end or terminal 177that extends outwardly into an opening in the lower end of the cathodestud 167, and specifically through an annular opening in the reducedportion 168 thereof and is mechanically and electrically connected tothe cathode stud 167, whereby the cathode structure 150 and the heater176 are both mechanically and electrically connected to the cathode stud167. The lower end of the heater 17 6 has an outer end or terminal 178that extends into an opening in the upper end of a conductor 197 and ismechanically and electrically secured thereto. The conductor 197 ispreferably formed of copper and extends outwardly and into a threadedconnector 196. It will be noted that the heater terminal 178 is spacedfrom and electrically insulated with respect to the lower end of thecathode structure 150.

Mounted within the outer ends of the anode sleeve 102 and forming endwalls for the device 100 are two internal pole pieces 130, the internalpole pieces 130 being identical in construction, whereby the samereference numerals have been applied to like parts of both of theinternal pole pieces 130. The internal pole pieces 130 are formed of amaterial having high magnetic permeability, the preferred material beinga low carbon steel, and are copper plated to render the outer surfacesthereof highly conductive to RF energy. As illustrated, each of theinternal pole pieces 130 is generally cylindrical in shape including afirst substantially flat inner plate 131 disposed centrally thereof anddisposed in a plane substantially normal to the longitudinal axis of thedevice 100 and in longitudinal alignment with the interaction space 160.Disposed about the periphery of the inner plate 131 and integraltherewith is a first annular coupling flange 132 extending outwardlytherefrom and carrying on the outer edge thereof an outwardly directedouter plate 133 that is substantially fiat and lying in a plane normalto the axis of the device 100 and being in longitudinal alignment withthe adjacent end of the outer axially extending space 120. The outeredge of the outer plate 133 carries a annular and outwardly extendingmounting and magnetic coupling flange 134 that has an outer diameterslightly less than the inner diameter of the associated recessed end ofthe anode sleeve 102 to be received therein and hermetically sealedthereto. Finally, there is provided centrally of each of the innerplates 131 a circular opening 135 in general longitudinal alignment withthe adjacent end of the cathode structure 150, and specifically theadjacent end of the cathode wall 151, the opening 135 receiving theterminals of the cathode structure and heater therethrough. Preferablythe internal pole pieces 130 are each formed of a single sheet of lowcarbon steel shaped as described by a samping operation, thereby toprovide accurate dimensions therefor together with an inexpensivemanufacture thereof.

Mounted about the outer ends of the anode sleeve 102 and in generallateral alignment with the internal pole pieces 130 are two externalpole pieces 140, the external pole pieces 140 being identical inconstruction, whereby the same reference numerals have been applied tolike parts of both of the external pole pieces 140. The external polepieces 140 are formed of a material having high magnetic permeability,the preferred material being a low carbon steel, and are copper platedto render the assembly thereof to the anode sleeve 102 readily possibleby a brazing operation. As illustrated, each of the external pole pieces140 is generally circular in shape and each includes a firstsubstantially flat plate 141 dlsposed in a plane substantially normal tothe longitudinal axis of the device and disposed in substantially thesame plane as the outer plate 133 of the associated internal pole piece130. The outer plate 141 has an opening centrally thereof circular inshape and having a diameter to receive therethrough the adjacent end ofthe anode sleeve 102. Disposed about the periphery of the opening in thecenter of the outer plate 141 and integral therewith is an annularcoupling flange 144 extending normal thereto and surrounding theadjacent end of the anode sleeve 102, the coupling flange 144 extendingfrom the associated outer plate 141 in the same direction that thecoupling flange 132 of the adjacent internal pole piece extends from theassociated outer plate 133 thereof. Preferably the external pole piecesare each formed of a single sheet of low carbon steel shaped asdescribed by a stamping operation, thereby to provide accuratedimensions thereof together with an inexpensive manufacture thereof.

As is illustrated in FIGS. 2 and 5 of the drawings, the upper internalpole piece 130 and the upper external. pole piece 140 cooperate toprovide an upper composite pole piece and the lower internal pole piece130 and the lower external pole piece 140 cooperate to provide a lowercomposite pole piece 145. Although the pole pieces 130 and 140 in eachof the composite pole pieces 145 are not in direct physical and magneticcontact one with the other, there is strong magnetic couplingtherebetween, it being pointed out that the sleeve 102 has a reducedwall thickness 106 disposed between the adjacent ones of the pole pieces130 and 140. Furthermore, the magnetic coupling flange 134 on each ofthe internal pole pieces 130 is disposed concentrically within andadjacent to the magnetic coupling flange 144 on the associated externalpole piece 140, thereby to provide a large mass of magneticallypermeable material that constitutes a low reluctance path for magneticlines of force between the adjacent ones of the pole pieces 130 and 140.

It further will be noted from FIG. 5 that the external diameter D of thecomposite pole pieces 145 is substantially greater than the gap betweenthe inner plates 131 of the internal pole pieces 130, and thus the gap Gthrough the interaction space more specifically, the ratio between theexternal diameter D of each composite pole piece 145 and the gap Gbetween the internal pole pieces 130 is approximately 2.25:1.Preferably, this ratio between the external diameter D of the compositepole pieces 145 and the length of the magnetic gap G between theinternal pole pieces 130 is in the range from about 2.0:1 to about2.511. It has been found that when the parts have the dimensions andratio of dimensions noted, a very strong and uniform field is providedthrough the interaction space 160, all provided in a structure that hassmall dimensions and that is inexpensive to manufacture.

An upper end structure is provided at the upper end of the device 100 asviewed in FIG. 2 and a lower end structure is provided at the lower endof the device 100, the end structures 180 and 190 serving to provide ahermetic seal between the associated internal pole pieces 130 and theassociated connections to the cathode structure 150 and/or the heater176, as the case may be. The upper end structure 180 includes a shorttube 181 having the lower end thereof disposed within the opening 135 inthe upper internal pole piece 130 and suitably hermetically securedthereto as by brazing and extending upwardly therefrom substantiallyconcentric with the longitudinal axis of the device 100 and the axis ofthe cathode stud 167. The upper end of the tube 181 receives therein thelower end of an annular insulator 182 which is formed, for example, of agood electrically insulating ceramic, the tube 181 being hermeticallysealed to the insulator 182. There is provided about the cathode stud167 at the portion thereof adjacent to the reduced portion 168 a ring183 that fits within a recess in the lower end of the insulator 182.Surrounding the upper end of the insulator 182 and the adjacent portionof the cathode stud 167 is a cap 185, the cap 185 being generallyannular in shape and including an annular flange 186 surrounding anouter periphery of the upper end of the insulator 182 and beinghermetically sealed thereto. Integral with the upper edge of the outerflange 186 is an inwardly directed flange 187 carrying on the inner edgethereof an outwardly directed annular inner flange 188 surrounding theadjacent portion of the stud 167 and hermetically sealed thereto as bybrazing. It is pointed out that the sleeve 181 and the cap 185 are bothformed of a material that can be readily secured both to a metal surfaceand to a ceramic surface, the preferred material being Fernico alloy, atypical composition being 54% iron, 28% nickel and 18% cobalt. It willbe seen that the upper end structure 180 forms a good hermetic seal thatalso provides electrical insulation between the upper internal polepiece 130 and the output conductor in the form of the cathode stud 167,the end structure 180 likewise providing the necessary mechanicalsupport for the cathode structure 150 to position it within the anodestructure 101.

In the lower end structure 190, a ceramic insulator 191 is provided thatis annular in shape and has an outer diameter just slightly less thanthe diameter of the opening 135 in the lower internal pole piece 130 andan inner diameter just slightly greater than the external diameter ofthe centering flange 159 on the lower cathode end 152, whereby theinsulator 191 serves to center the lower end of the cathode structure150 with respect to the lower internal pole piece 130. The insulator 191extends outwardly well beyond the lower internal pole piece 130 andthere is provided a seal member 192 annular in shape and surrounding theinsulator 191, the seal member 192 including a mounting flange 193fixedly secured as by brazing to the outer surface of the mner plate 131on the lower internal pole piece 130, the mounting flange 193 havingintegral therewith an annular wall 194 carrying an outer flange 195 thatis inwardly directed and surrounds and is secured to the outer wall ofthe insulator 191. The seal member 192 is made of the same material asthe sleeve 181 and the cap 185 and is hermetically sealed both to thelower internal pole piece 130 and the insulator 191. The outer end ofthe insulator 191 carries thereon a second seal member 198 that overliesthe outer end thereof and is suitably secured as by brazing to theconnector 196, the seal member 198 including an annular flange 199surrounding the outer end of the insulator 191 and sealed thereto. Theseal member 198 is formed of the same material as the seal member 192and is hermetically sealed both to the insulator 191 and the connector196. The lower end structure 190 therefore serves hermetically to sealthe lower end of the device 100 and also provides electrical insulationbetween the lower end of the cathode structure 150 and the associatedinternal pole piece 130 and the heater 176, all while providing for themechanical support of the lower end of the cathode structure 150' andthe lower end of the heater 176.

When the device 100 is incorporated as a crossed-field discharge devicein a microwave circuit, the composite pole pieces 145 arranged adjacentto the opposite ends of the anode structure 101 are utilized forestablishing a unidirectional magnetic field extending axially throughthe several spaces within the anode structure 101, and specificallythrough the axially extending space 120 and through the interactionspace 160, as well as the annular passage 123 and the various spacesbetween the anode members 110. To this end a pair of magnet coils 210and 215 has been-provided, the magnet coil 210 being disposed about theupper end of the device as viewed in FIG. 1 and the magnet coil 215being disposed about the lower end of the device 100 as viewed inFIG. 1. The magnet coils 210 and 215 are both shaped as a torous, arewound of electrically conductive wire, and as illustrated are disposedrespectively about magnet yokes 211 and 216, respectively, that includeinner annular sections cylinder disposed within the opening in theassociated magnet coil. There further are provided outwardly extendingend sections or flanges 213 and 218, respectively, about the outer endsof the inner sections 212 and 217 and secured respectively thereto. Itwill be understood that the magnet yokes 211 and 216, including theannular sections 212 and 217 and the end sections 213 and 218, are allformed of metals having a high magnetic permeability, such as soft ironand low carbon steel, whereby when the magnet coils 210* and 215 areenergized, a strong and uniform unidirectional magnetic field isestablished between the composite pole pieces 145 and extending axiallythrough the spaces within the device 100, and specifically extendingaxially through the outer axially extending space and the interactionspace 160 therein.

The circuit for energizing the coils 210 and 215 can be traced withreference to FIG. 1 from a DC power supply conductor 207a to a DC inputterminal 207 for the generator 10 to which is connected one terminal ofthe upper magnet coil 210. The other terminal of the upper magnet coil210 is connected by a conductor 214 to one terminal of the lower magnetcoil 215, and the other terminal of the lower magnet coil 215 isconnected by a conductor 219 to one of the cooling fins 108, whereby theinput terminal 207 is connected via the upper magnet coil 210, theconductor 214, the lower magnet coil 215, the conductor 219 and thecooling fin 108 to the anode sleeve 102 of the device 100. The flow ofcurrent through the magnet coils 210 and 215 serves to produce theunidirectional magnetic field in the various spaces of the device 100,and specifically in the outer space 120 and the interaction space 160thereof.

The crossed-field discharge device 100 and the magnet coils 210 and 215therefor, together with the other associated parts thereof, are allhoused within the box-like structure generally designated by the numeral200, see FIG. I particularly. The box-like structure 200 includes anupper end plate 201 and a lower end plate 205, the end plates 201 and205 being substantially rectangular in shape and having dimensionsslightly greater than the corresponding dimensions of the rectangularcooling fins 108. The end plate 201 is provided on one pair of sidesthereof with integral side flanges 202, the side flanges 202 beingdisposed substantially normal to the end plate 201 and extending towardthe lower end plate 205 and terminating just slightly below the loweredge of the upper magnet coil 210. The end plate 205 is provided on onepair of opposed sides thereof with integral side flanges 206, the sideflanges 206 being disposed substantially normal to the end plate 205 andextending upwardly toward the upper end plate 201 and terminating justslightly above the upper edge of the lower magnet coil 215. Enclosingthe space between the opposed free edges of the side flanges 202 and 206are side walls 203, the side walls 203 being disposed inside of theassociated ones of the side flanges 202 and 206 and being suitablysecured thereto. The other sides of the end plates 201 and 205 are free,whereby the associated sides of the box-like structure 200 are open toreceive therethrough a stream of cooling fluid, such as air, that passesaround the magnet coils 210 and 215 and around the cooling fins 108, itbeing noted that the external pole pieces also provide a certain amountof cooling for the device 100. In certain instances, it is desired tocover the open sides of the boxlike structure 200 with a foraminoussheet, such as a screen (not shown) in order to prevent inadvertentcontact with the high potentials present in the box-like structure 200.

In accordance with the present invention, the end plates 201 and 205 andthe side flanges 202 and 206 integral therewith are formed of a materialthat has a high magnetic permeability, such as soft iron and low carbonsteel, whereby these parts form a portion of a magnetic return path forthe magnetic circuit. The side walls 203, however, are preferably formedof a material having a low magnetic permeability, a preferred materialbeing aluminum, whereby the side walls 203 provide high reluctance pathsfor magnetic force lines. As a result, the set of opposed sides of thebox-like structure 200 on which are disposed the side walls 203 alsoappear to be open to the magnetic circuit as are the other set ofopposed sides of the box-like structure 200, whereby there issubstantially no distortion of the magnetic field within the device 100due to the presence of the materials of construction of the box-likestructure 200. As a result, a much more uniform magnetic field isprovided in the interaction space 160 than would be the case if the sidewalls 203 were formed of a material having a high magnetic permeability,whereby to provide a low reluctance magnetic path on one set of opposedsides of the boxlike structure 200 while providing a high reluctancemagnetic path on the other set of opposed sides of the box-likestructure 200. In this connection it is also pointed out that theexternal pole pieces 140 tend to shunt the leakage field that wouldotherwise tend to distort the magnetic field in the interaction space,the use of non-magnetic material for the side plates 203 tending tominimize leakage flux which would otherwise tend to saturate themagnetic yokes 211 and 216 and reduce the field intensity in theinteraction space 160.

Referring now to FIG. 1 of the drawings, the manner in which thecrossed-field discharge device 100 is incorporated in the generator willbe described in further detail. A tubular conductor 204 is providedformed of a material that is electrically conductive, the conductor 204having the lower end thereof received within the upper internal polepiece coupling flange 132 in telescoping relation therewith and iselectrically connected thereto, the conductor 204 also being disposedwithin the upper magnet yoke 211 and extending upwardly and beyond theupper end thereof. As is illustrated in both FIGS. 1 and 2, the cathodestud 167 at the upper end of the crossed-field discharge device 110 hasthe outer end thereof disposed below the outer end of the associatedmagnet yoke 211. The cathode stud 167 and the conductor 204 form acoaxial transmission line that provides output RF terminals for thegenerator 10, the terminals having applied therebetween the output RFenergy from the generator 10. In addition, the outer conductor 204 hasapplied thereto the B+ potential from the conductor 207a which isconnected thereto via the input terminal 207, the upper magnet coil 210,the conductor 214, the lower magnet coil 215, the conductor 219, thecooling fin 108, the anode sleeve 102 and the upper internal pole piece130, the upper internal pole piece 130 being directly connected to thelower end of the outer conductor 204 as illustrated. Accordingly, itwill be seen that the outer conductor 204 not only serves as one of theRF terminals for the device 100 but also is in direct electricalconnection with the B+ potential on the anode sleeve 102. Likewise, thecathode stud 167 not only has the RF output energy thereon but hasapplied thereto both the B potential for the cathode 150 of the device100 and the low voltage AC potential for energizing the heater 176.

In order to accommodate the application to and the presence of thevarious potentials named on the output terminals 167 and 204 whilepreventing the introduction of RF energy into the power supply 51, andwhile preventing the application of the B+ and B- potentials to theoutput terminals 231 and 241 provided, there has been provided a couplerand filter structure 230. Referring to FIG. 1, it will be seen that thecoupler and filter structure 230 includes a first RF output terminal inthe form of annular outer conductor 231 which is capacitively coupled tothe conductor 204 by a coupler 232, the coupler 232 including a sleeve233 of electrically insulating dielectric material, the sleeve 233preferably being formed of a synthetic organic plastic resin, thepreferred resin being a tetrafluoroethylene resin sold under thetrademark Teflon. The insulating sleeve 233 is disposed around andfirmly embraces the outermost end of the tubular conductor 204 andextends upwardly therebeyond; the lower end of the outer conductor 231is in turn placed in telescoping relationship about the sleeve 233, thelower end of the conductor 231 telescopically overlapping the upper endof the conductor 204 for a distance equal to A of the wavelength of thefrequency of operation of the generator 10 in order to provide a portionof a second harmonic filter.

An opening is provided in the side wall of the conductor 204 adjacent tothe upper end of the generator 10, and joining the conductor 204 andsurrounding the opening in the side wall thereof is a second annularconductor 234 that is suitably secured as by welding to the conductor204 and extends laterally therefrom and to the right as viewed in FIG. 1with the longitudinal axes of the conductors 204 and 234 disposedsubstantially normal to each other. Disposed in the conductor 204adjacent to the junction thereof with the conductor 234 is a pair ofannular insulators 235 and 236 substantially filling the conductor 204and spaced apart a short distance from each other, the insulators 235and 236 being formed of an electrically insulating dielectric material,the preferred material being a synthetic organic plastic resin, thepreferred resin being a tetrafluoroethylene resin sold under thetrademark Teflon. The lower insulator 235 has an opening centrallytherein that receives therethrough a portion of a bullet 237 having onthe lower end thereof a plurality of spring fingers 237a thatresiliently grip the upper end of the cathode stud 167 to form a goodelectrical contact and mechanical interconnection therewith, a laterallyextending flange 2237b extending around the bullet 237 and beingdisposed below and in supporting relationship with the insulator 235.

Extending upwardly through an opening in the center of the bullet 237 isa probe 238 in the form of a solid rod of electrically conductivematerial, the preferred material being copper. The probe 238 passesthrough an opening in the center of the insulator 236 and upwardlytherebeyond, the insulator 236 having an upstanding flange 236asurrounding the probe 238. A suitable fastener such as a screw 239 isprovided at the lower end of the probe 238 and threadedly engages acomplementarily threaded opening at the lower end thereof, the head ofthe screw 239 overlying the lower surface of the bullet 237. Arrangedabout and in telescoping relationship with the upper end of the probe238 is an annular inner conductor 240 that has the lower end restingupon the insulator 236 and surrounding the upstanding flange 236athereon, the upper end of the conductor 240 having an enlarged section240a thereon that extends upwardly well beyond the probe 238 andtelescopically receives therein a second tubular inner conductor 241that serves as an RF output terminal for the coupler and filterstructure 230, whereby the conductors 231 and 241 provide the RF outputterminals for the coupler and filter structure 230. A capacitivecoupling is provided between the probe 238 and the conductors 240 and241 by a coupler 242 including an annular washer 243 formed of anelectrically insulating dielectric material, the preferred materialbeing a synthetic organic plastic resin, the preferred resin being atetrafluoroethylene resin sold under the trademark Teflon. The washer243 surrounds the upper end of the probe 238 and is seated in theenlarged portion 240a at the upper end of the conductor 240 and servesfixedly to position the upper end of the probe 238 with respect to theconductors 240 and 241. A second fastener in the form of a screw 239 isprovided in the upper end of the probe 238 and has a threaded shankthreadedly engaged in a complementarily shaped threaded opening in theupper end of the probe 238, the head of the screw 239 engaging the uppersurface of the insulating washer 243, whereby the two opposed screws 239serve fixedly to interlock the insulators 235 13 V and 236, the bullet237, the conductor 240 and the insulating Washer 243.

The B- potential and the low voltage AC filament supply for the device100 are connected to the probe 238 and thus to the device 100 throughconnections in the conductor 234, and specifically through a conductor244 disposed within and concentric with the outer conductor 234. Theconductor 244 carries on the left hand end thereof as viewed in FIG. 1 aconnector 244a having an opening therein that receives therethrough theprobe 238, whereby to make good electrical connection therewith.Disposed about the conductor 244 and between the outer conductor 234 andthe inner conductor 244 is an annular insulator 245 formed of anelectrically insulating dielectric material, the preferred materialbeing a synthetic organic plastic resin, the preferred resin being atetrafluoroethylene resin sold under the trademark Teflon. Disposed tothe left of the insulator 245 is an enlargement or flange 244b on theconductor 244, and disposed to the right of the insulator 245 is acylindrical choke 246 in the form of a tubular conductor that surroundsand receives therethrough the conductor 244 arranged concentricallytherewith, the insulator 245 having a laterally extending flange 245asurrounding theconductor 244 and extending in the lefthand end of thechoke 246 to position the adjacent end of the choke 246 with respect tothe conductor 244. A conductive nut 247 is provided about the conductor244 adjacent to the righthand end thereof and including a flange 247aextending into the righthand end of the choke 246 to position theadjacent ends of the conductor 244 and the choke 246 with respect toeach other. The righthand end of the conductor 244 is threaded as at2440 and threadedly engages an internally threaded opening in the nut247 to lock the insulator 245 and the choke 246 against the flange 244b;the threaded end 2440 is connected to an input terminal 208 formed of aconductive metal, the terminal 208 having an enlarged lefthand end 249having a threaded opening therein to receive the adjacent threaded end2440 of the conductor 244. The terminal 208 extends outwardly to theright beyond the outer conductor 234 and is connected to a conductor208a from the associated power supply, the conductor 208a carrying boththe B" potential and the heater supply potential. Connected between theouter conductor 234 and the input terminal 208 is a filter capacitor 248of the feed through type that is in the form of two layers of conductivefoil between which are interposed layers of insulating film, the layersof conductive foil and insulating film being wound to form the capacitor248, one terminal of the capacitor 248 being connected to the outerconductor 234 and the other terminal of the capacitor 248 beingconnected to the terminal 208.

As has been explained above, the inner conductor 204 and the outerconductor 231 telescopically overlap a distance equal to A1 wavelengthof the frequency of operation of the generator 10. In addition, theprobe 238, the inner conductor 240 and the choke 246 are alsoconstructed to have a length equal to A Wavelength of the frequency ofoperation of the generator 10. In the operation of the coupler andfilter structure 230, the outer conductors 204234 serve as a B+ inputterminal, the con ductor 204 being directly connected to the conductor219 by which B+ potential is applied to the outer sleeve 102, and theterminal 208 services as the B input terminal and is connected to thecathode 150 via the conductor 244, the probe 248, the bullet 237, andthe cathode stud 167 (see FIG. 3 also), whereby to apply B potential tothe cathode 150. The terminal 208 also serves as an input terminal forthe low voltage AC filament supply and is connected to one end of theheater 176 via the conductor 244, the probe 238, the bullet 237 and thecathode stud 167, whereby to apply low voltage AC potential to the upperend of the heater 176.

The connector 196 at the lower end of the device 110 (see FIG. 2) isconnected to a filter capacitor of the feed through type, and morespecifically is connected to the input terminal 209 that has theadjacent end thereof internally threaded and receives the threaded outerend of the terminal 196 therein. A tubular conductor 221 is providedformed of a metal that is electrically conductive, the conductor 221having the upper end thereof received Within the lower internal polepiece coupling flange 132 in telescoping relation therewith and beingelectrically connected thereto, the conductor 221 being disposed-withinthe lower magnet yoke 216 and extending downwardly and beyond the lowerend thereof. There is provided on the lower end of the conductor 221 acover 222 formed of conductive metal and including a flange 224surrounding and in telescoping relationship with the lower end of theconductor 221 and mechanically and electrically secured thereto.Disposed between the terminal 209 and the cover 222 is a filtercapacitor 226 of the same type of construction as the filter capacitor248 described above, one of the terminals of the filter capacitor 226being connected to the cover 222 and the other terminal of the filtercapacitor 226 being connected to the terminal 209, a flange 227 beingprovided on the exterior of the filter capacitor 226 in overlyingrelationship with the cover 222. The filter capacitor 226 serves toby-pass RF energy from the terminal 209 to the outer conductor 221through the cover 222, thereby to prevent the introduc tion of RF energyinto the associated power supply via the conductor 209a.

Further details of the construction and a more full explanation of theoperation of the crossed-field discharge device and of the lower filter220 and the output coupler and filter structure 230 can be had byreference to the copending application for US. Letters Patent, Ser. No.559,267, filed June 21, 1966 by James E. Staats, the disclosure of saidapplication Ser. No. 559,267 being incorporated herein by reference.

The crossed-field discharge device of the above mentioned applicationSer. No. 559,267 when incorporated in a large magnet structure has anoperating efficiency of about 35%, but when that device is placed in acompact magnet structure, i.e., when the magnet coils were placed closeto the magnetic pole pieces within the device, the efliciency Wasreduced to about 30%. However, when the same device of application Ser.No. 559,267 was equipped with the external pole pieces of the presentinvention and was placed in the improved box-like structure 200incorporating the side plates 203 of non-magnetic material, theeffiicency thereof was increased to 40%, whereby it will be seen thatthe present invention presents a substantial increase in the efficiencyof the crossed-field discharge device.

In view of the foregoing, it is apparent that there has been provided acrossed-field discharge device and microwave assemblies incorporatingthe same that are of improved connection and arrangement, and whichfulfill all of the objects and advantages set forth above.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious modifications may be made therein and it is intended to cover inthe appended claims all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. A crossed-field discharge device comprising an envelope, an anodestructure disposed in said envelope and defining an axially extendingspace, an axially extending cathode structure disposed in said axiallyextending space and cooperating with said anode structure to define anaxially extending annular interaction space therebetween, said cathodestructure including an electron emissive element disposed within saidanode structure and adjacent to the inner portion of said interactionspace, a pair of internal identically constructed magnetic pole piecesdisposed interiorly of said envelope and respectively arranged adjacentto the opposite ends of said anode structure for establishing aunidirectional magnetic field extending axially through said interactionspace, and a pair of identically constructed external magnetic polepieces disposed exteriorly of said envelope and respectively arrangedadjacent to said internal pole pieces and in surrounding relationtherewith and extending radially outwardly therefrom, each one of saidinternal pole pieces cooperating with the adjacent one of said externalpole pieces to provide a composite pole piece, the dimensions of saidcomposite pole pieces normal to the axis of said interaction space beingsubstantially greater than the gap between said internal pole piecesaxially through said interaction space.

2. The crossed-field discharge device set forth in claim 1, wherein theportions of the wall of said envelope disposed between the adjacent onesof said pole pieces in each of said composite pole pieces is of lesserthickness than the remaining portions of the wall of said envelope todecrease the magnetic reluctance between the adjacent ones of said polepieces in each of said composite pole pieces.

3. The crossed-field discharge device set forth in claim 1, wherein saidinternal pole pieces are disposed at the opposite ends of said envelopeand provide the end caps therefor.

4. The crossed-field discharge device set forth in claim 1, wherein eachof said internal pole pieces has an axially extending annular flangethereon disposed against said envelope, each of said external polepieces has an axially extending annular flange thereon disposed againstsaid envelope; the flange on each of said internal pole pieces beingdisposed in radial alignment with the flange on the adjacent one of saidexternal pole pieces.

5. A crossed-field discharge device comprising an envelope, an annularanode structure disposed in said envelope and defining an annularaxially extending space, an axially extending annular cathode structuredisposed in said axially extending space and cooperating with said anodestructure to define an axially extending annular interaction spacetherebetween, said cathode structure including an electron emissiveelement disposed within said anode structure and adjacent to the innerportion of said interaction space, a pair of identically constructedannular internal magnetic pole pieces each having a generally circularperiphery and disposed interiorly of said envelope and respectivelyarranged adjacent to the opposite ends of said anode srtucture forestablishing a unidirectional magnetic field extending axially throughsaid interaction space, and a pair of identically constructed annularexternal magnetic pole pieces each having a generally circular peripheryand disposed exteriorly of said envelope and respectively arrangedadjacent to said internal pole pieces and in surrounding relationtherewith and extending radially outwardly therefrom, each one of saidinternal pole pieces cooperating with the adjacent one of said externalpole pieces to provide a composite pole piece, the outermost diameter ofsaid composite pole pieces normal to the axis of said interaction spacebeing substantially greater than the gap between said internal polepieces axially through said interaction space.

6. The crossed-field discharge device set forth in claim 5, wherein theratio between the outermost diameter of said composite pole piecesnormal to the axis of said interaction space and the gap between saidinternal pole pieces axially through said interaction space is in therange from about 2.0:1 to about 2.5: 1.

7. The crossed-field discharge device set forth in claim 5, wherein eachof said internal pole pieces has an axially extending annular flangethereon disposed against said envelope, each of said external polepieces has an axially extending annular flange thereon disposed againstsaid envelope, the flange on each of said internal pole pieces beingdisposed in radial alignment with the flange on the adjacent one of saidexternal pole pieces.

8. The crossed-field discharge device set forth in claim 5, wherein theportions of the wall of said envelope disposed between adjacent pairs ofthe flanges on said pole pieces being of lesser thickness than theremaining portions of the walls of said envelope to decrease themagnetic reluctance between the adjacent ones of said pole pieces ineach of said composite pole pieces.

'9. The crossed-field discharge device set forth in claim 5, whereinsaid anode structure defines therein an outer annular axially extendingspace enclosed thereby and an inner axially extending space extendingtherethrough and a radially extending passage interconnecting said outeraxially extending space and said inner axially extending space at thelongitudinal midsection of said anode structure, said radially extendingpassage dividing said anode structure into a first anode sectiondisposed adjacent to one end thereof and a second anode section disposedadjacent to the other end thereof, a plurality of axially extendinganode segments on the inner surfaces of said anode sections andprojecting radially into said inner axially extending space andproviding a corresponding plurality of axially extending anode recessestherebetween, a plurality of axially extending first rods on said firstanode section respectively disposed in the anode recesses in said secondanode section and respectively spaced from the adjacent ones of saidanode segments on said second anode section, and a plurality of axiallyextending second rods on said second anode section respectively disposedin the anode recesses in said first anode section and respectivelyspaced from adjacent ones of said anode segments on said first anodesection.

10. A crossed-field discharge device comprising an annular sleeve, apair of annular anode members disposed Within said sleeve, a pluralityof rods disposed adjacent to the inner surfaces of said anode members,said sleeve and said anode members being electrically connected at theopposite ends of said device and said rods being electrically connectedto said anode members at the outer ends thereof, said sleeve and saidanode members cooperating to define a first axially extending spacetherebetween and said anode members cooperating to define a secondaxially extending space therethrough and said anode members being spacedapart axially to provide a lateral passage therebetween interconnectingsaid axially extending spaces, each of said anode members having aplurality of radially extending anode segments on the inner surfacethereof projecting radially into said second axially extending space andproviding a plurality of axially extending anode recesses therebetween,said rods being respectively disposed in said anode recesses andrespectively spaced from the adjacent ones of said anode segments, anaxially extending cathode structure disposed in said second axiallyextending space and cooperating with said anode members to define anaxially extending annular interaction space therebetween, said cathodestructure including an electron emissive element disposed within saidanode members and adjacent to the inner portion of said interactionspace, a pair of identically constructed internal magnetic pole piecesdisposed interiorly of said sleeve and respectively arranged adjacent tothe opposite ends of said anode members for establishing aunidirectional magnetic field extending axially through said interactionspace, and a pair of identically constructed external magnetic polepieces disposed exteriorly of said sleeve and respectively arrangedadjacent to said internal pole pieces and in surrounding relationtherewith and extending radially outwardly therefrom, each one of saidinternal pole pieces cooperating with the adjacent one of said externalpole pieces to provide a composite pole piece, the dimensions of saidcomposite pole pieces normal to the axis of said interaction space beingsubstantially greater than the gap between said internal pole piecesaxially through said interaction space.

11. A microwave assembly comprising a crossed-field discharge deviceincluding an envelope, an anode structure disposed in said envelope anddefining an axially extending space, an axially extending cathodestructure disposed in said axially extending space and cooperating withsaid anode structure to define an axially extending annular interactionspace therebetween, said cathode structure including an electronemissive element disposed within said anode structure and adjacent tothe inner portion of said interaction space, a pair of internal magneticpole pieces disposed interiorly of said envelope and respectivelyarranged adjacent to the opposite ends of said anode structure forestablishing a unidirectional magnetic field extending axially throughsaid interaction space, a pair of external magnetic pole pieces disposedexteriorly of said envelope and respectively arranged adjacent to saidinternal pole pieces and in surrounding relation therewith and extendingradially outwardly therefrom, each one of said internal pole piecescooperating with the adjacent one of said external pole pieces toprovide a composite pole piece, the dimensions of said composite polepieces normal to the axis of said interaction space being substantiallygreater than the gap between said internal pole pieces axially throughsaid interaction space, and a plurality of radially extending coolingfins mounted on said envelope in good thermal contact therewith; a pairof annular field coils disposed with the axes thereof in alignment withthe longitudinal axis of said interaction space and respectivelyarranged adjacent to the opposite ends of said device for establishing aunidirectional magnetic field therebetween; a pair of magnetic yolresrespectively arranged about said field coils and each including an innersection extending longitudinally through the opening in the associatedfield coil and magnetically coupled to the adjacent one of said internalpole pieces, an end section arranged at the outer end of said innersection and magnetically coupled thereto and extending radiallyoutwardly therefrom beyond the periphery of the associated field coiland said cooling fins, and a pair of outer sections disposed on opposedsides of the associated field coil and magnetically coupled to said endsection and extending toward said device and terminating at pointsspaced outwardly and well away from the associated external pole piece;and side walls of non-magnetic material interconnecting the opposedpairs of said outer sections, said end sections and said outer sectionsand said side walls cooperating to provide a box-like structure Open ontwo opposed sides thereof and defining a passage for cooling air passingtherethrough and over said cooling fins and around said device to coolthe same.

12. The microwave assembly set forth in claim 11, wherein said coolingfins are formed of copper, and said side walls are formed of aluminum.

13. The microwave assembly set forth in claim 11, wherein said coolingfins and said end sections have substantially rectangular peripheries,and said outer sections are disposed on opposed sides of saidrectangular end sections.

14. A crossed-field discharge device comprising an envelope, an anodestructure disposed in said envelope and defining an axially extendingspace, an axially extending cathode structure disposed in said axiallyextending space and cooperating with said anode structure to define anaxially extending annular interaction space therebetween, said cathodestructure including an electron emissive element disposed within saidanode structure and adjacent to the inner portion of said interactionspace, a pair of identically constructed internal magnetic pole piecesdisposed interiorly of said envelope and respectively arranged adjacentto the opposite ends of said anode structure for establishing aunidirectional magnetic field extending axially through said interactionspace, each of said internal magnetic pole pieces comprising an annularinner plate disposed in a plane substantially normal to the longitudinalaxis of said device, a first annular axially extending flange disposedaround the periphery of said inner plate integral therewith andextending outwardly therefrom, an annular outer plate integral with theouter edge of said first flange and extending outwardly therefrom in aplane parallel to the plane of said inner plate and a second annularaxially extending flange disposed around the periphery of said outerplate and integral therewith and extending outwardly therefrom, and apair of identically constructed external magnetic pole pieces disposedexteriorly of said envelope and respectively arranged adjacent to saidinternal pole pieces and in surrounding relation therewith and extendingradially outwardly therefrom, each one of said internal pole piecescooperating with the adjacent one of said external pole pieces toprovide a composite pole piece, the dimensions of said composite polepieces normal to the axis of said interaction space being substantiallygreater than the gap between said internal pole pieces axially throughsaid interaction space.

15. A crossed-field discharge device comprising an envelope, an annularanode structure disposed in said envelope and defining an annularaxially extending space, an axially extending annular cathode structuredisposed in said axially extending space and cooperating with said anodestructure to define an axially extending annular interaction spacetherebetween, said cathode structure including an electron emissiveelement disposed within said anode structure and adjacent to the innerportion of said interaction space, a pair of identically constructedannular internal magnetic pole pieces each having a generally circularperiphery and disposed interiorly of said envelope and respectivelyarranged adjacent to the opposite ends of said anode structure forestablishing a unidirectional magnetic field extending axially throughsaid interaction space, each of said internal magnetic pole piecescomprising an annular inner plate disposed in a plane substantiallynormal to the longitudinal axis of said device, a first annular axiallyextending flange disposed around the periphery of said inner plateintegral therewith and extending outwardly therefrom, an annular outerplate integral with the outer edge of said first flange and extendingoutwardly therefrom in a plane parallel to the plane of said inner plateand a second annular axially extending flange disposed around theperiphery of said outer plate and integral therewith and extendingoutwardly therefrom, and a pair of identically constructed annularexternal magnetic pole pieces each having a generally circular peripheryand disposed exteriorly of said envelope and respectively arrangedadjacent to said internal pole pieces and in surrounding relationtherewith and extending radially outwardly therefrom, each one of saidinternal pole pieces cooperating with the adjacent one of said externalpole pieces to provide a composite pole piece, the outermost diameter ofsaid composite pole pieces normal to the axis of said interaction spacebeing substantially greater than the gap between said internal polepieces axially through said interaction space.

16. A crossed-field discharge device comprising an annular sleeve, apair of annular anode members disposed within said sleeve, a pluralityof rods disposed adjacent to the inner surfaces of said anode members,said sleeve and said anode members being electrically connected at theopposite ends of said device and said rods being electrically connectedto said anode members at the outer ends thereof, said sleeve and saidanode members cooperating to define a first axially extending spacetherebetween and said anode members cooperating to define a secondaxially extending space therethrough and said anode members being spacedapart axially to provide a lateral passage therebetween interconnectingsaid axially extending spaces, each of said anode members having aplurality of radially extending anode segments on the inner surfacethereof projecting radially into said second axially extending space andproviding a plurality of axially extending anode recesses therebetween,said rods being respectively disposed in said anode recesses and re-spectively spaced from the adjacent ones of said anode seg- 19 ments, anaxially extending cathode structure disposed in said second axiallyextending space and cooperating with said anode members to define anaxially extending annular interaction space therebetween, said cathodestructure including an electron emissive element disposed within saidanode members and adjacent to the inner portion of said interactionspace, a pair of identically constructed internal magnetic pole piecesdisposed interiorly of said sleeve and respectively arranged adjacent tothe opposite ends of said anode members for establishing aunidirectional magnetic field extending axially through said interactionspace, each of said internal magnetic pole pieces comprising an annularinner plate disposed in a plane substantially normal to the longitudinalaxis of said device, a first annular axially extending flange dissleeveand respectively arranged adjacent to said internal pole pieces and insurrounding relation therewith and extending radially outwardlytherefrom, each one of said internal pole pieces cooperating with theadjacent one of said external pole pieces to provide a composite polepiece, the dimensions of said composite pole pieces normal to the axisof said interaction space being substantially greater than the gapbetween said internal pole pieces axially through said interactionspace.

References Cited UNITED STATES PATENTS 2,787,728 4/ 1957 Crapuchcttes 31539.7l 3,158,780 11/1964 Gerlach 313158 X FOREIGN PATENTS 908,842 10/1962 Great Britain.

HERMAN KARL SAALBACH, Primary Examiner S. CHATMON, JR., AssistantExaminer US. Cl. X.R.

